The field of dental materials has benefitted greatly from basic research in inorganic, organic and polymer chemistry. Three major classes of dental materials have been developed and used in dental practice: (l) inorganic/ceramic materials (e.g. amalgams and silicate cements), (2) organic polymers (e.g. polyacrylate resins) and (3) polymer composite materials in which inorganic fillers are mixed with a polymer at a macroscopic level. All of these materials, though succeeded in some extent under constant modifications, have many inherent deficiencies in their dental applications. We have been interested in making a radical change of this situation by creating a novel class of dental materials. Funded by NIH (Grant No. ROl-DE09848) in the last 3 years, we have successfully synthesized such a class of dental materials, which covalently and uniformly incorporates organic polymers into inorganic matrices at the molecular level via the newly emerged sol-gel technology. These molecular composite materials demonstrated tailored combinations of the hardness of inorganic glasses and the toughness of organic polymers. There is no macroscopic phase separation in these materials so that the interface problems as exist in the conventional dental composites are eliminated. More excitingly, we discovered that the formation of these new materials can be achieved photochemically. This discovery is particularly important to the field of dental materials because one of the most common dental clinical practices is to cure the dental resins under ultraviolet radiation. In this proposal, we design a series of new in-depth studies to develop a fundamental understanding of the chemical/photochemical process that lead to the formation of these novel materials and to improve the synthesis and properties. Specifically, kinetic studies will be conducted on the photo-/nonphoto-catalyzed sol-gel reactions of the functionalized poly(methyl methacrylates) with the inorganic precursors silicon and/or titanium tetraalkoxides. The basic knowledge gained will be applied to design better synthetic strategies to solve the most challenging problems in the sol-gel reactions, i.e. volume shrinkage, cracking, and long curing time, all of which are highly undesirable in dental practice. The new synthesis will allow us to control and tailor the physical/chemical properties of this new class of materials even better for the dental applications. Moreover, the materials will be thoroughly characterized and tested. Their properties, such as hardness. toughness, adhesion to tooth structure, resistance to wear and abrasion, stability etc. will be directly compared with the existing dental composite materials. The success of this research will lay the foundation for future clinical application of this new class of materials.